Network Monitor

Performance Tools

Responsive Design Mode

See how your website or app will look and behave on different devices and network types.

These developer tools are also built into Firefox. Unlike the "Core Tools" above, you might not use them every day.

Memory Figure out which objects are keeping memory in use. Storage Inspector Inspect cookies, local storage, indexedDB, and session storage present in a page. DOM Property Viewer Inspect the page's DOM properties, functions, etc. Developer Toolbar A command-line interface for the developer tools. Eyedropper Select a color from the page. Scratchpad A text editor built into Firefox that lets you write and execute JavaScript. Style Editor View and edit CSS styles for the current page. Shader Editor View and edit the vertex and fragment shaders used by WebGL. Web Audio Editor Examine the graph of audio nodes in an audio context, and modify their parameters. Taking screenshots Take a screenshot of the entire page or of a single element. Measure a portion of the page Measure a specific area of a web page. Rulers Overlay horizontal and vertical rulers on a web page

If you open the developer tools using keyboard shortcuts or the equivalent menu items, they'll target the document hosted by the currently active tab. But you can attach the tools to a variety of other targets, too, both within the current browser and in different browsers or even different devices.

Debugging the browser

By default, the developer tools are attached to a web page or web app. But you can also connect them to the browser as a whole. This is useful for browser and add-on development.

Browser Console See messages logged by the browser itself and by add-ons, and run JavaScript code in the browser's scope. Browser Toolbox Attach the Developer Tools to the browser itself.

The developer tools are designed to be extensible. Firefox add-ons can access the developer tools and the components they use to extend existing tools and add new tools. With the remote debugging protocol, you can implement your own debugging clients and servers, enabling you to debug websites using your own tools or to debug different targets using the Firefox tools.

Firebug is coming to the end of its lifespan (see Firebug lives on in Firefox DevTools for details of why), and we appreciate that some people will find migrating to another less familiar set of DevTools to be challenging. To ease a transition from Firebug to the Firefox developer tools, we have written a handy guide — Migrating from Firebug.

Contribute

If you want to help to improve the developer tools, these resources will get you started.

Get Involved Mozilla wiki page explaining how to get involved. firefox-dev.tools A tool helping to find bugs to work on.